Galaxy Imaging Success: Tips and Tricks

One of the joys of deep sky astrophotography is galaxy imaging. These are not always easy targets but are well worth the effort. Just think for a moment, photographing something millions of light years away that contains billions of stars, countless planets, and perhaps inhabited worlds so far away we can only dream of going there.

In this post, I am going to show you how to image a galaxy and what problems you may encounter when trying to do this. We’ll discuss how you can overcome these problems and capture the best details possible with the equipment you have. We’ll also consider several popular galaxies and consider how easy or difficult they are to image.

I’ll also show you what I have learned in my efforts to photograph various galaxies and what I plan to image next. Remember also that there are many kinds of galaxies. If you want to image them, you should learn about lenticular galaxies and others you can observe through a telescope.

How to photograph galaxies

There are two ways to image a galaxy in deep space. The first is to take many photographs with a DSLR camera and lens, stack them, and processing the image. The second is to use a camera and a good telescope together, stack, and process. The results will depend on your equipment, the amount of time you spend photographing it, and your image processing skills.

Recommended Telescopes for Galaxy Imaging

Before making some specific suggestions for telescopes that are good for imaging galaxies, let’s discuss what kinds of telescopes are best.

What Type of Telescope is best for Photographing Galaxies?

You have several choices:

• A reflector telescope
• A refractor
• A Schmidt- Cassegrain telescope
• A smart telescope

If you are looking for the cheapest option, then that is probably a Newtonian reflector¹. These are great for photographing galaxies but there is often one major problem. Many reflectors, like the one I use (Celestron 130slt), will not allow you to reach focus when you attach a camera. This is because many reflectors are designed for viewing and can only be used for astrophotography by either cutting the tube or moving the primary mirror. Read more about this problem and how I solved it.

A good solution is to buy a refractor as it is quite easy to attach a camera for astrophotography. A Scmidt- Cassegrain is an excellent choice for imaging galaxies but is a bit more expensive.

The easiest way to do astrophotography in general, including photographing galaxies, is to use a smart telescope. These are high tech and reasonably priced.

How to Choose a telescope for Galaxy Imaging

Before looking at specific models you can use, let’s look at what you need to look for in a suitable astrophotography telescope.

There are two important parts of an astrophotography telescope setup, the OTA (the telescope tube which you can buy alone) or the OTA plus the mount. For astrophotography you should buy an equatorial mount² . This will enable you to take longer exposures which are necessary to photograph faint objects like distant galaxies.

The telescope OTA needs to have a focal length long enough to capture the many small galaxies out there. My telescope has a focal length of 650mm, and I have to crop and zoom my images to see the details of most galaxies. The larger the focal length the closer you will zoom into a galaxy. However, longer focal lengths need better tracking. I would advise getting something in the 800-2000mm range.

The focal ratio is also important. My telescope OTA is F5 which is good. For capturing the light from distant galaxies we need a low focal ratio. The lower it is the more quickly your telescope will collect the light needed for your photo. Therefore, imaging time is reduced. Telescopes can vary between about F2 and F10.

Also, it is a good idea to consider how portable your telescope is. You may wish to take it to a place with a dark sky to improve your images. Therefore, think carefully before buying heavier and larger equipment unless you plan to image from a permanent location such as a backyard pier or observatory.

Specific Telescope Models for Imaging Galaxies

This OTA is a good choice:

• Celestron 9.25″ SCT (don’t get it with an alt-az mount)

Like mine, this one has a shorter focal length but that’s OK:

SVBONY SV503 Telescope

• 102mm aperture
• ED glass 
• Doublet, achromatic
• Sharp quality image

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Telescope and Mount together:

• Celestron Edge Hd8 8″ SCT

Celestron – Advanced VX 8” EdgeHD Computerized Telescope

• 203mm aperture
• equatorial mount
• 2030mm focal length
• weighs 85 pounds

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Generally, when researching what astrophotographers use and what they discuss on forums, refractors of aperture size 80mm seem to be a good starting point for imaging the larger galaxies like the Andromeda. 100mm refractor telescopes will be better for smaller galaxies and anything over 120mm starts to be what you really want for more detail. Larger refractors get heavier, larger and more expensive.

As for Newtonian reflectors, Orion has a great selection that are suitable for astrophotography and for galaxies. Check out their VX range of telescope OTAs which range in cost from hundreds to thousands of dollars.

What are the best camera settings for galaxy imaging?

If you use a DSLR you should set your camera to manual focus. You’ll need quite a high level for ISO and this will depend on your camera specifications. I use a Canon 600D and found that ISO 800 was the best but you could go higher to bump up the camera signal. Galaxy imaging is tough because galaxies are very faint so a high ISO and long exposure time of at least 60 seconds is best.

If you can use a good quality mount or star tracker then galaxy imaging improves when you expose for several minutes. If the weather is calm, I set my exposure time to five minutes which is long enough to capture good signal and lower the noise. However, if it is windy I lower this to two or three minutes. This is exactly what I did last night when imaging the Hamburger Galaxy and the Whale galaxy. This is despite using autoguiding. The wind cannot be corrected by autoguiding it is too random and fast.

Set your shutter to the most open position (the lowest focal ratio or F stop you can get) as this will let more light into your camera and onto the camera sensor. This will lower the amount of time you need to expose to get a good image.

The other camera settings you should select are to enable mirror lock up if you have a DSLR with a mirror and turn off automatic noise reduction as that takes a dark frame after each photograph reducing the amount of time you have for galaxy imaging. The benefit is not worth the gain you’ll get from more integration time.

If you are using, as I do, an astronomy camera you should set the gain to the correct value which is most efficient and has the least amount of noise. You can look this up for your camera. For my ZWO ASI533 MCPRO camera I set it to 100 gain.

The other important camera setting for my camera is the cooling temperature which I always set to zero degrees. I don’t see any point in going any lower. It uses a lot of power and doesn’t make a lot of difference to the level of noise.

Astrophotography Techniques for Galaxy Imaging

Here are some of the main challenges that you may face when trying to image galaxies:

• Galaxies are so faint that you cannot easily see them until you have either taken a sufficiently long exposure or stacked together several images. This will make it difficult to know if you have centred the galaxy in your field of view or not.
• Light pollution can reduce the contrast in your galaxy image. The correct filter can help.
• Galaxies are very faint because they are so far away from us so capturing the details is not easy.
• Processing a galaxy image is a challenge. The processing technique is different from that required to create images of a nebula or other deep sky objects.

Most of these issues can be overcome by following the techniques in the following section. Experience in processing and taking images of various galaxies will help you to improve your skills so that each time you return to a galaxy, you will be able to obtain a better result. As with most things in astrophotography, using your own equipment is the best way to improve.

Here’s a great DSLR for capturing those galaxies:

Canon EOS Rebel T7 DSLR Camera and two lenses

• 24.1 MP resolution
• Built-in Wi-Fi
• 1080p video
• 18-55mm and 75-300mm lenses
• Approx. $600

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I do have some suggestions for how to overcome some of the above issues, but I am also still learning how to perfect my methods of galaxy imaging. Recently I have made great progress!

Before reading on, it might be a good idea to read this about seeing galaxies through a telescope.

How to Locate and Center a Galaxy

Let’s discuss how to improve your galaxy imaging by addressing some of these challenges and I’ll offer tips from my experience where I can.

Before galaxy imaging, there are a few things you can do that will help you improve your images.

The first problem is locating and centering your galaxy. I tried at first to locate galaxies by trying to see them but this is almost impossible as most galaxies cannot be seen easily without a huge telescope. How can you take an excellent image without being able to find your galaxy, you can’t. So what’s the solution?

The best way to find a galaxy is to align your telescope using star alignment, slew to the galaxy’s coordinates, and then take test photos to see if you can image the galaxy. Then you’ll need to centre the galaxy in your field of view. 

One better solution I now use is plate-solving, which removes a lot of the guesswork from this. It also saves a huge amount of time. The coordinates of your target galaxy are enough to find it with a tool like the Astrophotography Tool (this is the tool I use, but others prefer software such as NINA, etc.). Plate-solving not only locates your galaxy, but it also places it exactly in the centre of your field of view.

How to Deal with Light Pollution

Light pollution is unfortunately an issue with galaxies because certain wavelengths of light that are given off by artificial light, such as streetlamps, are also present in your target. This means that using certain filters may impact your galaxy imaging. I have found that this is more important for certain galaxies than others. I had problems using an Astronomik CLS filter when imaging the Andromeda Galaxy and fixed this by using an Ioptron L-Pro filter which worked much better.

If light pollution is a problem in your imaging location, then you may need to use a filter, so choose carefully and experiment to make sure, as I did, that it does not negatively affect your galaxy imaging. Here’s some help with choosing the right filter for astrophotography.

The best solution for this is to go to a dark location and try imaging the galaxy higher up in the sky without a filter and then use your post-processing skills to remove any gradient or light pollution in your image. This should give you a much better result. As many say, the best filter for astrophotography is the gas filter!

I’ll return to the topic of filters below as they are not only used to reduce the effect of light pollution, but they can also enhance your image.

Stacking Long Exposures to Reveal Galaxy Details

Because galaxies are so far away, they cannot normally be seen with the naked eye. However, we can take long exposures of several minutes to reveal them in an image. I’ve found that 3-5-minute-long exposures works well in my Bortle 5 sky.

One long exposure frame of a few minutes will not give you a very good image, so we use a technique called stacking. This technique uses software to stack many photographs together. When I image a galaxy I choose my exposure time for each frame and then I continuously take shots through the night. I aim for several hours, the more the better. I have found that the best images of galaxies need at least five or six hours of total integration time.

To help you choose your exposure time, use my calculator.

To shoot long exposures continuously either use a remote shutter with a DSLR camera or use software like Astrophotography Tool with an astronomy camera, (can also be used with a DSLR). You’ll need to set the exposure time and the number of images you want to shoot.

It’s a good idea to take calibration frames which will improve your final image. These frames remove noise and problems with dust in your telescope or camera optics. Find out more about calibration frames here.

To stack the images, you’ll need to check them to make sure they have no star trails and are in focus. Next, use software such as Deep Sky Stacker or my preferred choice Siril.

This will help you find those wonderful galaxies:

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How to capture detailed images of distant galaxies?

Techniques vary according to your astrophotography target, and galaxies are no different. My techniques may be very different from someone else’s. Astrophotography involves experimentation, and this improves your images by enabling you to understand how to get the best from the equipment you have. In other words, my suggestions here are a summary of what has worked for me and what I have learned about imaging galaxies successfully, although no one can claim to have fully mastered this.

Here are my suggestions to you, and I hope they help you to improve on your last image, or if this is your first, to get something you will be happy with.

First, figure out which field of view you need to best frame the galaxy. I took a great picture of the Andromeda Galaxy with my Samyang 135mm camera lens (a great lens for astrophotography). The galaxy is a little small, but the whole of the galaxy can be captured nicely to create a fantastic image. Capturing it with my telescope at 650mm was too close and did not enable me to capture the whole galaxy. One solution to this is to create a mosaic and image the galaxy by taking two or more separate images and then joining them together.

If you use manual methods to locate the galaxy, it will appear as a fuzzy blob in a raw image from your camera. Don’t expect much until you stack and stretch it.

If you use plate solving it’s much quicker (five minutes or so) and much easier! I recommend you try it.

Make sure you watch videos and read about how best to image and process galaxies; there is a lot of more detailed information out there for this. Here are two suggestions for further research:

• Photographing Andromeda by Trevor Jones
• And this excellent article from SkyandTelescope

For removing light pollution and gradients, I recommend Gradient Xterminator, Astr Flat Pro, and others that also exist, but these are the ones I know really work and will improve your images.

How do I process and edit galaxy images?

Now I’d like to talk a bit specifically about a few image processing techniques that can really make a difference in your galaxy images.

Which filters can I use when Imaging galaxies?

Basically, you can use a broadband filter such as the Ioptron L-Pro that will cut out some of the light pollution but not much of the precious light you want.

Some galaxies benefit from hydrogen alpha data. I am trying this with the Cigar Nebula and will try it with a few others too. It has added some colour to my image of the Triangulum Galaxy (M33), which you can see below. For this, you can use either a hydrogen-alpha filter (I have used the Astronomik HA 12nm clip-in filter with my DSLR and a ZWO Duoband 15nm filter with my dedicated astro camera).

The below image was taken by combining hydrogen alpha with RGB using a ZWO ASI533 MC PRO camera.

I took 34 x 6-minute exposures of both RGB and Narrowband (HA and Oiii). Tracked with Ioptron CEM26 and guided. I was very happy with the result! Taken in 2022. Check this page to learn more about autoguiding.

Which galaxies are the easiest to image?

I’ve included this section because you might be asking this question if you are imaging galaxies for the first time, but even if you do have some experience, this is an important question to answer, I think.

Here are some of the easiest, most of which I have imaged myself:

• M31 – The Andromeda Galaxy This is our closest neighbor—so close in fact that it will collide with us 4.5 billion years from now. It can be seen with the naked eye in a dark location (I’ve seen it in Bortle 3/4).
• Triangulum Galaxy (see my image above), also known as M33 is quite easy to image and can be clearly seen in a raw exposure on your DSLR. It looks like a blurry, swirling cartwheel but is faint in one shot.
• Sombrero Galaxy. I have only imaged this one time and want to return to this target again as my processing skills have improved and my equipment has been upgraded. The image below was taken with an Alt-Az mount.

I’d like to add one important challenge you can sometimes face and in particular I faced this while imaging Andromeda Galaxy.

Andromeda has a very bright core but the outer areas of the galaxy are dim. So how can we best image this galaxy? If you image for, say, five minutes to capture the faint details, the core of the galaxy will be blown out and over exposed spoiling your image. What’s the solution?

In order to solve this problem, you need to take some shorter exposure images, perhaps 30 seconds, for the brighter core area and combine these with longer exposures to capture the fainter details, such as the arms of the galaxy. You can then combine the two in your image processing workflow. This is very similar to the process I used to capture the Orion Nebula, which also has a very bright core.

Comparison of different popular galaxies imaged by astrophotographers

Rough Guide for Galaxies – How Long Should Sub-Exposures and Integration Time Be?

The length of sub-exposures and total integration time required for galaxy imaging will depend on various factors, such as the equipment being used, the environmental conditions, and the desired level of detail in the final image. That being said, I can give you general guidelines for sub-exposure and total integration time for the galaxies you listed in your previous question.

So, use the following as a starting point and modify your settings as necessary. As always, after some experimentation and testing, you will see what works and what doesn’t. But these settings should help get you started:

The figures above are for broadband RGB-type filters or without a filter. For narrowband, it is normally necessary to multiply sub-exposure lengths³. I would triple the sub-exposure time if you plan to do narrowband to collect hydrogen alpha, for example. Again, just a suggestion. Find what works best for you and your setup and conditions.

And to help you learn how to produce stunning galaxy images:

Star-gazing Guide to Photoshop Astrophotography Image Processing

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Conclusion

So, there you have it! Based on what I have managed to image so far and the research I have done, you can take the information above and use it to develop your own method suitable for your equipment, location, and conditions at the time when you image your galaxy.

I’m sure that after a few tries, you’ll be able to get a result that pleases you. There is always room to improve, and that will come with time. Enjoy your galaxy imaging!

References

1. Am Scope. Refractor telescope vs Refractor: which is right for you? https://amscope.com/blogs/news/refractor-telescope-vs-reflector-telescope-which-is-right-for-you
2. Astro Pix. Mounts for Astrophotgraphy. https://www.astropix.com/html/astrophotography/mounts.html
3. Tucker, S. (2020) Narrowband imaging, Starizona. Available at: https://starizona.com/blogs/tutorials/narrowband-imaging